Homocysteine Test
The homocysteine test measures total plasma homocysteine, an amino acid cleared via folate-, B12-, and B6-dependent pathways. It serves as a functional marker of B-vitamin status, helps confirm functional B12 deficiency, and is an independent but modest cardiovascular and thrombotic risk marker.
1
Biomarkers
Blood (plasma)
Sample
2–4 business days
Turnaround
Yes — a fasting morning sample is preferred, as recent protein intake can transiently raise homocysteine
Fasting
What is the Homocysteine test?
The Homocysteine Test measures total plasma homocysteine, an amino acid whose clearance depends on folate, vitamin B12, and vitamin B6. Elevations reflect impaired metabolism from nutritional deficiency, renal dysfunction, or inherited enzyme defects, making the test useful both as a functional marker of B-vitamin status and as a cardiovascular and thrombotic risk marker. Within the assessment landscape, homocysteine sits between nutritional and cardiovascular testing. As a metabolic marker it helps confirm functional B12 deficiency when total B12 is borderline, complementing methylmalonic acid, and it indicates folate or B6 inadequacy. As a vascular risk marker it is an independent but modest predictor of atherosclerotic and thromboembolic disease, used selectively rather than as a routine screen, since lowering homocysteine with B vitamins has not consistently reduced cardiovascular events. Markedly elevated values prompt evaluation for homocystinuria or related inherited disorders. Because the analyte is labile, specimen handling materially affects the result.
What does the Homocysteine test measure?
Homocysteine is a sulphur-containing amino acid formed during the metabolism of methionine. It is cleared by two vitamin-dependent routes: remethylation to methionine, requiring folate and vitamin B12, and transsulphuration to cysteine, requiring vitamin B6. Because these pathways depend on B-vitamin cofactors and adequate renal clearance, plasma homocysteine rises when any of these is deficient or impaired. It circulates largely protein-bound, and the analyte is labile in whole blood, continuing to be released from red cells if the specimen is not processed promptly.
Total homocysteine is a sensitive functional marker of folate, B12, and B6 status and an independent, if modest, risk marker for cardiovascular and thromboembolic disease. Markedly elevated levels raise suspicion of inherited disorders such as homocystinuria or MTHFR-related metabolism, while moderate elevations more often reflect nutritional deficiency or renal impairment. It is also used to help confirm functional B12 deficiency when total B12 is equivocal.
Why is the Homocysteine test ordered?
- Confirmation of functional B12 deficiency where total B12 is low-normal or equivocal, interpreted alongside methylmalonic acid
- Assessment of suspected folate, B12, or B6 deficiency as a functional metabolic marker
- Evaluation of unexplained venous or arterial thromboembolism where hyperhomocysteinaemia is a consideration
- Investigation of suspected inherited metabolic disorders — homocystinuria or severe MTHFR-related metabolism — particularly with markedly elevated levels or suggestive clinical features
- Cardiovascular risk profiling in selected patients with premature or unexplained atherosclerotic disease
- Assessment of patients with renal impairment where homocysteine is commonly elevated and informs the metabolic picture
- Monitoring of homocysteine-lowering with B-vitamin repletion in patients with documented hyperhomocysteinaemia
Sample collection and turnaround
Sample type
Blood (plasma)
Fasting required
Yes — a fasting morning sample is preferred, as recent protein intake can transiently raise homocysteine
Collection method
Venipuncture at patient service centre
Turnaround
2–4 business days
Collection notes
Specimen is labile — collect into the specified anticoagulant tube, chill immediately, and separate plasma promptly to prevent ongoing red-cell release of homocysteine, which falsely raises the result. Document B-vitamin supplementation and relevant medications.
Specimen requirements
Minimum 1.0 mL plasma. Collect on ice, separate plasma from cells promptly (per LabCorp protocol, typically within 30–60 minutes), and freeze for transport. Do not use unprocessed whole blood held at room temperature.
What can affect Homocysteine results?
Homocysteine continues to be released from red cells in uncentrifuged whole blood, so delay between collection and separation spuriously raises the result. The specimen should be chilled and plasma separated promptly per protocol.
These vitamins are cofactors for homocysteine clearance via remethylation and transsulphuration. Deficiency of any of them impairs metabolism and raises plasma homocysteine — the basis of its use as a functional nutritional marker.
The kidneys contribute to homocysteine metabolism and clearance, so reduced renal function commonly raises levels independent of vitamin status.
Genetic variants reducing enzyme activity in the methionine pathway raise homocysteine, with severe defects causing marked hyperhomocysteinaemia and homocystinuria.
Drugs that interfere with folate or B12 metabolism, or impair their absorption, can raise homocysteine. Medication history should be documented.
Folate, B12, and B6 supplementation lowers homocysteine, so recent supplementation may mask an underlying deficiency or normalise a previously elevated value. Supplementation status should be recorded.
What do Homocysteine results mean?
Elevated
Moderate elevation most often reflects folate, B12, or B6 deficiency, or renal impairment. Marked elevation raises suspicion of an inherited disorder such as homocystinuria. In the vascular context, elevation is an independent but modest risk marker, and the cause — nutritional, renal, or genetic — should be sought before attributing significance.
Normal
A normal homocysteine makes clinically significant folate, B12, or B6 deficiency less likely and argues against marked metabolic or inherited disorders. Recent supplementation can normalise the value, so it should be interpreted with the dietary and treatment history.
Reduced
Low homocysteine has no recognised adverse clinical significance and may reflect recent B-vitamin supplementation. It is generally regarded as favourable in the cardiovascular context.
Note: Specimen handling is critical — delayed separation spuriously elevates results, so prompt chilling and centrifugation are essential. Homocysteine is non-specific, rising with nutritional deficiency, renal impairment, genetic variants, and drugs. Its role as a cardiovascular risk marker is modest, and lowering it with B vitamins has not reliably reduced cardiovascular events, so it is used selectively and interpreted alongside B12, folate, and renal function.
Frequently asked questions
It measures total plasma homocysteine, an amino acid cleared by folate-, B12-, and B6-dependent pathways. It is used as a functional marker of B-vitamin status and as a modest, independent cardiovascular and thrombotic risk marker.
How to access the Homocysteine test
The Homocysteine reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: June 2, 2026
Last reviewed: June 2, 2026
- Refsum H, et al. Facts and recommendations about total homocysteine determinations: an expert opinion. Clin Chem. (2004)
- Clarke R, et al. Homocysteine and Coronary Heart Disease: Meta-analysis of MTHFR Case-Control Studies. PLoS Med. (2012)
- Martí-Carvajal AJ, et al. Homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database Syst Rev. (2017)
- Devalia V, et al. Guidelines for the diagnosis and treatment of cobalamin and folate disorders. Br J Haematol. (2014)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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